IonExchange Separation and Spectrophotometric Determination of Nickel and Cobalt

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Ion-Exchange Separation and
Spectrophotometric Determination of Nickel and
Cobalt

• By Doan-Phuong Dao

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Background information

• This experiment had two major steps
• 1)Separation of Ni and Co in the unknown sample
  by using an ion-exchange chromatography column
  with a strong base anion exchanger
• 2) Determination of the concentrations of Ni and
  Co in the unknown sample by using standard
  spectrophotometric procedures

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Ion exchange chromatography

• In ion-exchange chromatography, retention is
  based on the attraction between solute ions and
  the charged sites bound to the stationary phase.
• In anion exchangers, positive charged groups on
  the stationary phase attract solute anions
• Cation exchangers contain covalently bound,
  negatively charged sites that attract solute
  cations
• This experiment used a strong base anion exchanger

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• In solution containing a large concentration of
  hydrochloric acid, Co was converted into complex
  anions (chlorides) CoCl4 2-, and was adsorbed by
  an anion resin. Ni was not converted into complex
  anions so that it was not adsorbed by such a
  resin. The separation of Nickel from Cobalt was
  easily effected. The cobalt is removed by washing
  the resin with 1M HCl.

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• After separating from the mixture, Nickel was
  oxidized with bromine in ammonia solution and
  then treated with dimethylglyoxime. A wine-red or
  brown complex is formed. Cobalt was determined by
  conversion of the metal to the blue complex
  cobalt thiocyanate, Co(CNS)42-.
• 95 ethanol solution was used because both
  complexes were somewhat dissociated in water
• The concentrations of Ni and Co were determined
  by measuring the absorbance at 455 nm (for Ni),
  and at 625 nm (for Co) with a spectrophotometer.
  

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• The graphs of concentration vs. absorbance of Ni
  and Co standard solution were plotted to
  determine the line equations.
• From the line equations , the absorbance of the
  Ni and Co in the unknown were plugged in to
  calculate the concentration of each metal in the
  sample

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Question

• What is required when it comes to separating
  Nickel and Cobalt in the column?

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Answer

• Need 9M HCl to bind to Cobalt and release Nickel
• Need 1M HCl to release the Cobalt from the column.